Steel yourself - Silver test is
not copper bottomed
Cross my stamps with silver? Not likely.
One of the problems with philately is that once something is established as ‘fact’ it gets repeated again and again no matter how stupid, or simply wrong, it is.
Take the idea of checking for chalky paper. I will lay you an empire to an empty promise that you have read at least a dozen times that the test is to mark the surface of the stamp with a piece of silver.
If the paper is chalky that will leave a black mark on your precious stamp.
I wonder if anyone has actually done it. The trouble I would have is a lack of ready silver, but would not want to destroy a stamp by putting black lines on it anyway, even if they can supposedly be rubbed out.
There again, I don't need to worry as it doesn't work anyway.
There are problems at both ends.
At one end is what goes in to the mixture which gives the paper what philatelists call a chalky surface. There isn’t a consistent mixture and some of the ingredients were bizarre. For example, Edward VII GB stamps were coated with a mixture of chalk, lactose extracts, ammonia, milk and a developer which was made up of mometol and hydroquinone. At the other end is silver itself. Silver reacts with very few things, and certainly not with any of the contents of 'chalky paper'.
Indeed, it only reacts to air slowly and that is only with the sulphur compounds in the air which is why silver tarnishes.
So why does silver sometimes make a mark on chalky papers? Well in the olden days when you spoke of silver people would take a sixpence or shilling out of their pocket. It would have been well-circulated, by which I mean dirty and tarnished.
Now, as just mentioned, the tarnish is caused by sulphides from the air. It is the sulphides which are causing the reaction, not the silver.
There is another problem, particularly for used stamps. The so-called silver test, if it worked at all assumes the chalky surface is still on the stamp and the sulphides are reacting to it.
However, when you soak a stamp off paper sometimes a thin film can come off as well - that was the chalky surface. So testing for it with a little piece of silver in your hand is pointless. It has gone down the plughole.
So how can you see if your stamp was produced on chalky paper? Take a good look at it.
Dealers and others can often tell by touch or sometimes you can see the chalk surface by holding the stamp to the light and looking across it, if it is glossy it it chalky.
A better way is to either get a powerful magnifying glass or, better, scan stamps into your computer and enlarge them.
A lot of writers say that adding the chalky surface closed up the loose fibres on the surface of the paper. That's not right. Part of the process of surfacing the paper was to pass it though heavy rollers, this is called calendering, which closes up the loose fibres on the surface.
The important thing for us is that once the paper is squashed by the rollers and coated the ink on it tends to stay put, that is to say, it does not colour in the microscopic rough fibres, because there either isn't any or there are far fewer of them.
Here are two scans of a GB Edward VII 2d stamp, both produced by De La Rue. The one on the left is ordinary paper so the coloured outside line is fairly blurry - it is called bleed - the overlap on the right is on chalk-surfaced paper so there is much less bleeding, the line is clearer and sharper:
Something else to look out for are microscopically small holes on the surface of chalk-coated papers. Some of the elements used to produce chalky paper caused the printing plate to become pitted. I find them quite difficult to see and how pitted a plate became depended on how long it was used for, but others swear by this method.